1. Field of the Invention
The present invention relates to exercise apparatus, and more specifically to an exercise apparatus that guides a user's feet through automatically adjustable paths of motion.
2. Description of Related Art
Running on treadmills remains a popular form of indoor aerobic exercise even though it can lead to injuries. A runner hops from foot-to-foot, stressing his or her lower extremities with repetitive impact forces of each footfall that can eventually injure joints and tendons. Running the equivalent of only ten miles per day on a treadmill can expose each leg to 200,000 impacts per year. Many other kinds of exercise apparatus, including stationary bicycles, steppers, climbers, gliders and skiers, provide indoor aerobic exercise that allow a user's feet to follow a closed path without the impact stress associated with treadmills, however despite the advantages of these apparatus, running on treadmills remains popular. Since people are structurally better adapted to run rather than to pedal, climb steps, glide or ski, they often feel more comfortable running.
Elliptical exercise apparatus include foot support or pedals following closed paths designed to mimic the non-circular paths a user's feet trace out when running on a treadmill, but since the user's feet do not leave the foot supports, the user can engage in a running style of exercise without experiencing the repetitive impacts associated with running on a treadmill. Since the user's feet follow paths that are neither linear nor circular, they are commonly called “elliptical” paths to distinguish them over the circular closed paths provided stationary bicycle apparatus and the linear or arcuate closed paths associated with steppers and skier, gliders and climbers, even though an elliptical exercise apparatus normally does not provide a truly elliptical foot path.
A typical elliptical exercise apparatus includes a crank moving in a circular motion and a linkage mechanism coupling the crank to its foot supports for converting the circular motion of the crank into the “elliptical” motion of the foot supports. The linkage also includes a resistance device such as a regenerative or eddy current brake coupled to the crank for providing an adjustable resistance to the foot motion for controlling the amount of work the user must expend to move the foot supports. Examples of elliptical exercise apparatus are disclosed in U.S. Pat. No. 4,185,622 to Swenson; U.S. Pat. No. 5,278,529 to Eschenbach, U.S. Pat. No. 5,383,829 to Miller; U.S. Pat. No. 5,540,637 to Rodgers, Jr.; U.S. Pat. No. 6,196,948 to Steams et al.; and U.S. Pat. No. 6,468,184 to Lee, all of which are incorporated herein by reference.
The height and length of a runner's stride varies depending on running speed, on the terrain and on the runner's preferences. While early elliptical exercise apparatus designs allowed a user to engage in a running style of motion while avoiding the impact stress associated with treadmills, the shape of the path the user's foot followed was fixed and the user was not able to adjust either the height or length of stride. Later elliptical exercise apparatus designs allowed a user to adjust stride length. For example U.S. Pat. No. 5,893,820 issued Apr. 13, 1999 to Maresh et al. describes an elliptical apparatus allowing a user to adjust the shape of an elliptical footpath by manually changing the linkage between the crank and the foot supports. U.S. Pat. No. 5,919,118 issued Jul. 6, 1999 to Steams et al. teaches to incorporate a linear actuator into the linkage that can expand or contract to change the shape of the linkage in response to a signal controlled by a user-operable button on a control panel, thereby to change stride length. Although these apparatuses allow a user to adjust stride length, they required the user to stop the apparatus and manually alter the linkage, or to operate a control knob or button while exercising, either of which is inconvenient.
Still later designed elliptical exercise apparatuses automatically adjust stride length or height. U.S. Pat. No. 6,206,804 issued Mar. 27, 2001 to Maresh describes an elliptical exercise including dampers or springs in the linkage assembly defining the user's footpath that automatically vary the path shape in response to forces applied by the user's foot. U.S. patent application 20050181911, filed Aug. 18, 2005 by Porth teaches an elliptical exercise apparatus that senses the speed at which the crank rotates in which the crank rotates and adjusts an actuator in the linkage so that both stride length and height change with speed and pedaling direction. While the apparatus automatically adjusts stride length or height, there is no assurance that stride length or height that is adjusted as a function of speed or direction will match the user's desired stride length or height.